On the nature of amorphous polymorphism of water

We report elastic and inelastic neutron scattering experiments on different amorphous ice modifications. It is shown that an amorphous structure (HDA') indiscernible from the high-density phase (HDA), obtained by compression of crystalline ice, can be formed from the very high-density phase (vHDA) as an intermediate stage of the transition of vHDA into its low-density modification (LDA'). Both, HDA and HDA' exhibit comparable small angle scattering signals characterizing them as structures heterogeneous on a length scale of a few nano-meters. The homogeneous structures are the initial and final transition stages vHDA and LDA', respectively. Despite, their apparent structural identity on a local scale HDA and HDA' differ in their transition kinetics explored by in situ experiments. The activation energy of the vHDA-to-LDA' transition is at least 20 kJ/mol higher than the activation energy of the HDA-to-LDA transition

Arthroscopic repair of posterosuperior rotator cuff tears with bioabsorbable patch augmentation: a magnetic resonance–controlled case series with 1-year follow-up

Background: Among many advances in the treatment of rotator cuff tears, arthroscopic augmentation techniques with patches of various biological and synthetic graft materials have been introduced to reinforce the repair. However, structural and functional outcomes after patch augmentation vary, and reinforcing the tendon healing remains a challenge. The aim of this study was to evaluate clinical and radiologic outcomes 1 year after arthroscopic posterosuperior (PS) rotator cuff repair with bioabsorbable patch augmentation. Methods: From October 2014 to December 2017, all patients with PS rotator cuff tears undergoing arthroscopic repair with patch augmentation using a resorbable, biologically derived poly-4-hydroxybutyrate patch (Biofiber; Wright, Memphis, TN, USA) were enrolled in this study. Only full-thickness PS lesions with ≥1 of the following tear patterns were augmented with a patch and were the subject of this study: large U- and L-shaped tear, transtendinous tear, delamination, and fraying of the bursal layer. Patients were examined preoperatively and at 1 year postoperatively with a standardized examination protocol and magnetic resonance imaging (MRI). Results: Sixteen patients were included in this study; 1 patient was lost to follow-up. One patient only underwent clinical follow-up. We detected 1 repair failure (6.7%) with dislocation of the lateral-row anchors on computed tomography scanning at 3 months postoperatively. MRI was performed in 14 patients after 1 year; in all of them, the cuff repair was intact. The Sugaya tendon integrity score was 1.7 ± 0.9. The Constant-Murley score improved from 44 to 89 points (P < .001). Muscular strength improved in the supraspinatus (from 2.6 to 4.8), infraspinatus (from 3.2 to 4.9), and subscapularis (from 4 to 4.9) (all P < .001). Overall, patient satisfaction was high (3.6 ± 0.6). Discussion: This small-sized case series is the first to prospectively assess clinical and radiologic outcomes after patch augmentation of PS rotator cuff tears using bioabsorbable poly-4-hydroxybutyrate patches. Good to excellent structural and functional outcomes were observed with a low retear rate (6.7%) and good tendon integrity on 1-year postoperative MRI, and the graft did not cause any complications. The use of bioabsorbable patches could be beneficial when unfavorable PS tear patterns are encountered in which a stable repair of the full tendon thickness at its insertion is otherwise difficult to reach

Partial sacrectomy with patient-specific osteotomy guides

Background Chordomas are rare, locally aggressive, malignant tumors. Surgical resection with sufficient margins defines the outcome. However, the necessity for wide margins often leads to sacrifice of important neurological structures. 3D-printed osteotomy guides are a promising solution for precise execution of surgical resection. We present probably the first sacrococcygeal chordoma resection with 3D-printed guides. Methods The case of a 49-year-old woman with a sacrococcygeal chordoma, resected with help of 3-D pre-operative planning and patient-specific 3D-printed osteotomy guides, is reported in detail. Results A sufficient tumor excision could be performed successfully while sparing nerve root S4. The planed margin has been exactly maintained, as confirmed by histology. The patient demonstrated an excellent clinical outcome with no evidence of local recurrence. Conclusions 3-D pre-operative planning and patient-specific osteotomy guides can be used for planning and performing en-bloc surgical resection of sacral chordomas

Clinical relevance of occult infections in spinal pseudarthrosis revision

BACKGROUND Occult infections in spinal pseudarthrosis revisions have been reported in the literature, but the relevance of such an infection on patient outcomes is unknown. We aimed to elucidate clinical outcomes and re-revision risks between patients with and without occult infections in spinal revision surgery for pseudarthrosis. METHODS In this matched case-control study, we identified 128 patients who underwent thoracolumbar revision surgery from 2014-2019 for pseudarthrosis of the spine. Among them, 13 (10.2%) revealed an occult infection (defined by at least two positive intraoperative tissue samples with the same pathogen), and nine of these 13 were available for follow-up. We selected 18 of the 115 controls using a 2:1 fuzzy matching based on fusion length and length of follow-up. The patients were followed up to assess subsequent re-revision surgeries and the following postoperative patient-reported outcome measures (PROMs): overall satisfaction, Oswestry Disability Index, 5-level EQ-5D, and Short Form 36. RESULTS Patient characteristics, surgical data, and length of follow-up were equal between both study groups. The rate of re-revision free survival after the initial pseudarthrosis revision surgery was higher in the occult infection group (77.8%) than the non-infectious controls (44.4%), although not significantly (0.22). The total number of re-revision surgeries, including re-re-revisions, was thirteen (in ten patients) in the control and two (in two patients) in the occult infection group (p = 0.08) after a median follow-up of 24 months (range 13-75). Four cases in the control group underwent re-revision for pseudarthrosis compared to none in the infected group. Satisfactory scores were recorded in all PROMs, with similar scores between the two groups. CONCLUSIONS The presence of an occult infection accompanying spinal pseudarthrosis revision was not inferior to non-infected pseudarthrosis revisions in a matched, small sample size cohort study. This may be explained due to the possibility of targeted treatment of the identified cause of pseudarthrosis

Operator independent reliability of direct augmented reality navigated pedicle screw placement and rod bending

Background AR based navigation of spine surgeries may not only provide accurate surgical execution but also operator independency by compensating for potential skill deficits. “Direct” AR-navigation, namely superposing trajectories on anatomy directly, have not been investigated regarding their accuracy and operator's dependence. Purpose of this study was to prove operator independent reliability and accuracy of both AR assisted pedicle screw navigation and AR assisted rod bending in a cadaver setting. Methods Two experienced spine surgeons and two biomedical engineers (laymen) performed independently from each other pedicle screw instrumentations from L1-L5 in a total of eight lumbar cadaver specimens (20 screws/operator) using a fluoroscopy-free AR based navigation method. Screw fitting rods from L1 to S2-Ala-Ileum were bent bilaterally using an AR based rod bending navigation method (4 rods/operator). Outcome measures were pedicle perforations, accuracy compared to preoperative plan, registration time, navigation time, total rod bending time and operator's satisfaction for these procedures. Results 97.5% of all screws were safely placed (<2 mm perforation), overall mean deviation from planned trajectory was 6.8±3.9°, deviation from planned entry point was 4±2.7 mm, registration time per vertebra was 2:25 min (00:56 to 10:00 min), navigation time per screw was 1:07 min (00:15 to 12:43 min) rod bending time per rod was 4:22 min (02:07 to 10:39 min), operator's satisfaction with AR based screw and rod navigation was 5.38±0.67 (1 to 6, 6 being the best rate). Comparison of surgeons and laymen revealed significant difference in navigation time (1:01 min; 00:15 to 3:00 min vs. 01:37 min; 00:23 to 12:43 min; p = 0.004, respectively) but not in pedicle perforation rate. Conclusions Direct AR based screw and rod navigation using a surface digitization registration technique is reliable and independent of surgical experience. The accuracy of pedicle screw insertion in the lumbar spine is comparable with the current standard techniques

Pedicle subtraction osteotomy with patient-specific instruments

Background Although the utility of patient-specific instruments (PSI) has been well established for complex osteotomies in orthopedic surgery, it is yet to be comparatively analyzed for complex spinal deformity correction, such as pedicle subtraction osteotomy (PSO). Methods Six thoracolumbar human cadavers were used to perform nine PSOs using the free-hand (FH) technique and nine with PSI (in total 18 PSOs). Osteotomy planes were planned on the basis of preoperative computed tomography (CT). A closing-wedge angle of 30° was targeted for each PSO. Postoperative CT scans were obtained to measure segmental lordosis correction and the deviation from the planned 30° correction as well as the osseous gap of posterior elements. Results The time required to perform a PSO was 18:22 (range 10:22–26:38) min and 14:14 (range 10:13–22:16) min in the PSI and FH groups, respectively (p = 0.489). The PSI group had a significantly higher lordosis gain (29°, range 23–31° vs. 21°, range 13–34°; p = 0.015). The lordosis gain was significantly more accurate with PSI (deviation angle: 1°; range 0–7°) than with the FH technique (9°; range 4–17°; p = 0.003). PSI achieved a significantly smaller residual osseous gap of the posterior elements (5 mm; range 0–9 mm) than the FH group (11 mm; range 3–27 mm; p = 0.043). With PSI, an angular difference of 3° (range 1–12°), a translational offset of 1 (range 0–6) mm at the level of the lamina, and a vertebral body entry point deviation of 1 (range 0–4) mm was achieved in the osteotomies. Conclusions PSI-guided PSO can be a more feasible and accurate approach in achieving a planned lordosis angle than the traditional FH technique in a cadaver model. This approach further reduced osseous gaps, potentially promoting higher fusion rates in vivo